Elastomeric articles free from reinforcing elements

ABSTRACT

Pneumatic tires and other elastomeric articles subject to tensile stress and dynamic flexure in service, said articles having no reinforcing elements, or having reinforcing elements in portions only thereof, are made from elastomers having, in the cured state, a molecular weight between covalent cross-links of 5,100 - 40,000, and a molecular weight between electrostatic cross-links of 800 - 5,000. Such articles exhibit excellent strength, elasticity, tear resistance, flat-spotting properties and overall performance in service, both at ambient and elevated temperatures.

United States Patent McGillvary I [54] ELASTOMERIC ARTICLES FREE FROMREINFORCING ELEMENTS [72] Inventor? Daniel R. McGillvary, Massillon,

Ohio

[73] Assignee: The Firestone Tire & Rubber Company, Akron, Ohio [22]Filed: July 6, 1970 [21] Appl. N0.: 52,150

[52] US. Cl. ..152/330, 74/231 P, 92/34, 138/177, 260/775 AM, 260/82.l[51] Int. Cl. ..C08g 22/04, B60c 5/00 [58] Field of Search 260/77.5 AM,94.2 R, 77.5, 260/82.1; 152/330 [5 6] References Cited UNITED STATESPATENTS 3,208,500 9/1965 Knipp et a1. ..152/327 [15] 3,701,374 [451 Oct.31, 1972 OTHER PUBLICATIONS Athey, Rubber Age, 85, No. l, 1959, pp. 77-81 Buist et al., Advances in Polyurethane Technology, Maclaren & Sons,Ltd, London, 1968, pp. 42- 53 Primary Examiner-Donald E. Czaja AssistantExaminer-M. J. Welsh Att0rneyS. M. Clark and Willard L; G. Pollard 5 7]ABSTRACT Pneumatic tires and other elastomeric articles subject totensile stress and dynamic flexure in service, said articles having noreinforcing elements, or having reinforcing elements in portions onlythereof, are made from elastomers having, in the cured state, amolecular weight between covalent cross-links of 5,100 40,000, and amolecular weight between electrostatic cross-links of 800 5,000. Sucharticles exhibit excellent strength, elasticity, tear resistance,flat-spotting properties and overall performance in service, both atambient and elevated temperatures.

8 Claims, 3 Drawing Figures ELASTOMEREC ARTHCLES FREE FROM IREHNIFORCHNGELEMENTS BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to pneumatic tires, air springs, power transmissionbelts, and other articles subjected to tensile stresses and dynamicflexure in service, at least portions of which articles are free fromreinforcing fabrics. in some of its more particular aspects, theinvention relates to the production of such articles by molding fromflowable materials, as by centrifugal cast ing, injection molding,transfer molding and like processes.

2. Description of the Prior Art Pneumatic tires, air springs, hoses,transmission belts and other articles subject to tensile stresses anddynamic flexure in service are conventionally fabricated by laying up ofplies of elastomeric materials containing textile reinforcing textileelements. It would be highly desirable to dispense with the reinforcingelements, as it would then be possible to mold the article directly fromthe elastomeric material, or a precursor thereof, in flowable form,rather than to go through the laborious lay-up procedures required toplace the reinforcing textile elements in their required location in thearticles. it has not heretofore been practical to dispense with thereinforcing elements, however, because the elastomer compositionsavailable have not had the requisite high modulus, tensile strength,tear resistance and creep resistance in conjunction with flex resistancethat would be required in such articles not containing textilereinforcing elements. it will be appreciated that the flex resistance onthe one hand, and the modulus, tensile, tear and creep resistance on theother hand, are mutually antagonistic properties, and that it isdifficult to secure satisfactory values of all of these propertiessimultaneously in a single stock.

Accordingly, it is an object of this invention to provide elastomericstocks having the physical properties required in articles from whichthe reinforcing elements have been partially or entirely omitted.Another object is to provide such a stock which, prior to vulcanization,is readily flowable, so that articles may be formed therefrom bycentrifugal casting, injection molding, transfer molding and the like.

SUMMARY The above and other objects are secured, in accordance with theinvention, in pneumatic tires, air springs, hoses, power transmissionbelts and other articles subjected to tensile stresses and dynamicflexure in service, said articles being partially or wholly withoutreinforcing textile elements. These articles are made from elastomericstocks of the type having, in cured form, both covalent cross-links andalso electrostatic cross-links, van der Waals forces or otherintermolecular association cross-links, hereinafter referred to aselectrostatic cross-links. The composition and curing conditions of theelastomeric material are so selected that A. the molecular weight of thepolymeric chains between the electrostatic cross-links is 800-5 ,000,and preferably LOGO-3,000, and

B. the molecular weight of the chains between covalent cross-links is5,l0O40,000 and preferably 10,000-20,000.

Such cured elastomers have physical properties requisite for articles ofthe types referred to, or portions of such articles, without thenecessity for includ ing reinforcing textile elements therein, andspecifically, have the following key physical properties:

Tensile strength at 2l2F. (100C) 2 1800 psi Crescent tear strength at2l2F. (l00C.) z 200 pounds/inch DeMattia flex life at 176F. (C.) 2 2X10cycles 2 signifies equal to or greater than Advantageously, elastomersmeeting the above requirements may be made, by techniques describedbelow, from precursors which are readily flowable, so that tires andother articles according to this invention may be prepared bylow-labor-cost centrifugal, injectionand transfer-molding processes.Particularly, the articles of this invention may be constituted ofelastomeric polyurethanes made from poly(alkylene glycols) end-cappedwith diisocyanates and cured with diamines and/0r diols substantially inexcess of the usual sub-stoichiometric quantities.

THE DRAWING in the drawing FIG. 1 is a sectional view of a tireaccording to this invention, completely without any reinforcingelements;

FIG. 2 is a sectional view of a tire according to this invention,wherein reinforcing cords are provided at the interface between the bodyof the tire and a tread portion in the area of the tread only, thesidewalls being without any reinforcing elements, and

FIG. 3 is a sectional view of a tire according to this invention,wherein reinforcing cords are provided at the interface between the bodyof the tire and a tread portion in the area of the tread, and alsoextend for a substantial distance down the sidewalls, the remainder ofthe sidewalls being without any reinforcing elements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The Elastomers Used in ThisInvention Elastomers suitable for use in this invention include anygenerally linear high polymers, the chains of which are of elastomericcharacter, i.e., having second order transition temperatures below about20 C., and which contain groupings along the chains capable of formingelectrostatic space force cross-links and also groupings capable offorming true covalent cross-links. in many cases the same groupings arecapable of establishing either one of these types of cross-links.Suitable elastomers include the (preferred) polyurethane rubbers,particularly those formed by capping the hydroxyls of polyalkyleneglycols of molecular weight in the range of 800-2,500'with diisocyanatesto form prepolymers, and then chain-extending and curing the prepolymersby means of diamines and/or diols. Suitable polyalkylene glycols areexemplified in poly(alkylene glycols) having molecular weights in therange of 800-2,500 based on alkylene groups of from two to 10 carbonatoms such as poly(ethylene glycol), poly(propylene glycol),poly(trimethylene glycol),

poly(tetramethylene glycol), poly(hexamethylene glycol), high molecularweight copolymers of these glycols, and mixtures of the variouspoly(alkylene glycols) individually falling within the above categories.Suitable diisocyanates are exemplified in com pounds having twoisocyanate groups linked to an organic residue of six to 16 carbon atomssuch as hexamethylene diisocyanate, the various tolylene diisocyanates,the various naphthalene diisocyanates, 4,4- diphenylmethanediisocyanate, 3,3-dimethyl-4,4'- diphenylmethane diisocyanate,4-diphenyl-isopropylidene diisocyanate, 3,3-dimethyl-4,4-biphenyldiisocyanate, the phenylene diisocyanates, 3,3-dimethoxy- 4,4-biphenyldiisocyanate, and the like. Suitable diamines are those containing anorganic central radical of two to 20 carbon atoms linked to two aminogroups such as ethylene diamine, tetramethylene diamine, hexamethylenediamine, p-phenylenediamine, methylene-bis-2-chloroaniline (MOCA"), 4,4-diaminodiphenylmethane, 3,3'-dichloro-4,4- diaminodiphenylmethane,benzidine, 3,3'-dimethylbenzidine, 3,3-dimethoxy benzidine, 3,3-dichlorobenzidine, and the like. In these rubbers the chains of curedpolymer contain the repeating linkage R NHCO NHR -NCCO-O wherein J Prepresents a high molecular poly(alkylene ether) chain derived from apoly(alkylene glycol) such as specified above;

R is the organic radical of a diisocyanate such as specified above and Ris the organic central radical of a diamine such as specified above.

Electrostatic cross-links tend to form between the CO groups and ethergroups and the hydrogen atoms on the nitrogen atoms on adjacent chains;and the isocyanate groups of the prepolymer react in a certainproportion with these hydrogen atoms to form covalent crosslinks. It isthe control of the magnitude and proportions of the respective amountsof these two types of crosslinks that underlies the criticalcharacteristics of the articles of this invention. A particularadvantage of the preferred polyalkylene glycol/diisocyanate/diaminebasedelastomers is the fact that prior to final crosslinking, they areflowable for a sufficient period of time so that they may be formed bycentrifugal, injection or transfer molding into the form of the desiredarticle. With flow-molding processes of these types, it is extremelydifficult to include reinforcing cord, hence the rubbers of thisinvention are particularly advantageous in the cured state because theyare able to function in an article subject to tensile and dynamicflexure stresses without the presence of reinforcing cords.

Besides the ether urethanes, there may also be employed polyesterurethanes, and also other elastomers capable of establishing bothelectrostatic and covalent cross-links, such as copolymers of (A)butadiene, isoprene, acrylic esters or other monomers, polymeric chainsfrom which are of essentially elastomeric character with (B) monomerscontaining salt-forming groups such as acrylic acid, methacrylic acid,maleic acid, fumaric acid, itaconic acid and the like.

The Electrostatic Cross-Links and the Covalent Links betweenelectrostatic cross-links equalling 800 to 5000 (preferably 1000 to3000) and Molecular weight of polymer chains between covalentcross-links equalling 5100 to 40,000

(preferably I The methods of ascertaining these two characteristicsinvolve known solvent swelling procedures described generally in Cluffet al., J. Pol. Sci. 45 pp. 341-345 (1960). Swelling proceduresinvolving non-polar solvents such as chloroform reflect the spacing ofelectrostatic cross-links, since non-polar solvents do not disrupt suchcross-links. Swelling procedures conducted in polar solvents, such astetrahydrofurane, on the other hand, reflect the spacing of the covalentcross-links, since the electrostatic cross-links are dissociated by suchsolvents. It will be understood, therefore, that the conformity-or notof a rubber to this invention is to be ascertained with respect toelectrostatic cross-links by swelling measurements conducted inchloroform or some other non-polar solvent; and with respect to covalentcross-links, by swelling measurements conducted with tetrahydrofurane orsome other polar solvent capable of dissociating electrostaticcross-linkages.

Regarding the formulation and curing of elastomers so as to develop thetypes of cross-links desires, the factors influencing these parametersare well understood by those in the art. With particular reference tothe preferred polyurethanes discussed above, it is necessary to useunconventionally high ratios of curing amine to free isocyanate in theprepolymer, say about 0.98-1.08 equivalents of diamine* The equivalentweight of a diamine is one-half of its molecular weight.) per equivalentof isocyanate in the prepolymer. Within this range the molecular weightbetween covalent cross-links will increase to a maximum, and adjustmentscan be made up and down as may appear desirable. The molecular weightbetween electrostatic crosslinks is in general an increasing function ofthe molecular weight of the poly(alkylene glycol) employed, and thisfactor can be increased and decreased by selection of higher or lowermolecular weight poly(alkylene glycol) starting materials. Likewiselower curing tem- I peratures tend to increase the molecular weightbetween covalent cross-linkages. Generally temperatures in the rangel25-325 F. (51l63 C.) will be employed, and adjustment of the molecularweight between cross-links can be further adjusted by varying the curingtemperature within this range.

Physical Properties of the Elastomers The elastomers used in the tiresof this invention have the following critical properties.

21800 psi 2200 pounds/inch 2 10' cycles These properties are extremelyimportant in themselves for a rubber in a tire or other articlesubjected to tensile stress and dynamic flexure in service unsupportedby reinforcing cord, and they moreover, in the experience with theinstant invention, have been found to entrain the following propertiesat ambient temperatures (ca. 25 C.) which are also of great importancein this context:

Modulus of elongation of:

250-400 psi at 5% elongation 1 100-1300psi at 100% elongation 1400l550psi at 200% elongation l600-1800psi at 300% elongation 2000-2200psiat 400% elongation 2800-3500psi at 500% elongation Tensile strength22800 psi Elongation 400% Youngs flexural modulus 10,000-1 5,000 psiDETAILED DESCRIPTION OF THE DRAWINGS Referring now more particularly toFIG. 1, there is shown a cross section of a pneumatic tire indicatedgenerally at 10, having a body comprised of sidewalls 12 and anunder-tread portion 13, all made from the elastomer of the typespecified hereinabove, and all devoid of any reinforcing cords. The headportions 25 have bead wires 14 running therearound. A tread portion 16is shown as a separate body of rubber adhered to the under-tread-portion13 and also devoid of reinforcing cords; in many cases this will be thesame identical composition as the body 12, 13, and in such cases it willbe, of course, continuous with the body 12, 13. Mother cases, it may bedesired to apply a separate tread portion of a composition moreparticularly designed for that service, with emphasis on abrasion resistance, road traction, noise abatement, etc. Since there are noreinforcing cords to complicate operations, the tire may be readilyformed, from liquid elastomer precursor compositions meeting thecriteria of this invention, by centrifugal casting. The head wires 14may be supported in place by small blocks of precured elastomer, or bypins in the mold, during the casting operation. In those cases where thetread portion 16 is of a composition difierent from the main body 12, 13of the tire, the portion 16 may be formed by either initially pouring aliquid elastomer precursor of the desired composition, or by laying in asolid band of the desired composition and configuration, and thenpouring the precursor for the main body 12, 13.

Referring to FIG. 2, this shows a pneumatic tire having sidewalls 22,22, bead wires 24, and under-tread portion 27 similar to the elements12, 12, 14 and 13 respectively of the tire of FIG. 1. However, in thisembodiment the tread portion 26 has reinforcing cords 28 imbeddedtherein at the interface between the tread portion 26 and theunder-tread portion 27 to strengthen the tread portion and/or confinethe squirming action of the tread. The tire of FIG. 2 may bemanufactured by making the tread portion 26 as a solid preform with thecords 28 imbedded therein, inserting the same into a centrifugal mold,and then pouring the liquid elastomer precursor in accordance with thisinvention. It will be appreciated that this is still a relatively simpleoperation compared to the customary drumbuilding operation, as thefabrication of the shallow band 26 is readily automated. It will beunderstood that the sidewall portions 22 do not contain reinforcingcords, and that the elastomer in these portions must have the propertiesset forth hereinabove.

Referring now to FIG. 3, this shows a pneumatic tire comprising sidewallportions 32, under-tread portion 37, bead wires 34 and tread portion 36reinforced with cords 38, corresponding respectively with the elements22, 27, 24, 26 and 28 of FIG. 2, except that in this case the cords 38,instead of being confined to the immediate tread portion as in the caseof FIG. 2, extend for a substantial distance down the sidewalls to thepoints 40. This construction can be manufactured by the procedure oflaying the cord-containing tread and partial sidewall portion 36 intothe centrifugal mold as a solid preform, followed by centrifugal castingof the remainder of the tire as in the case of FIG. 2. Again it will beappreciated that the sidewalls 32, below the termination 40 of thereinforcing cords 38, must be made of an elastomer having the propertiesset forth hereinabove.

With the foregoing general discussion in mind, there are given herewithdetailed examples of the practice of this invention.

SWELLING DETERMINATION OF MOLECULAR WEIGHT BETWEEN CROSS-LINKS Theswelling test used in determining the molecular weight betweencross-links in the examples hereinbelow was an adaptation of theprocedure of Cluff et al. J. Polymer Sci. 45, pp. 341-45 (1960).Specimens were prepared by casting the finally compounded rubbers ofExample I hereinbelow, while still flowable, into 1 inch test tubes,which were then heated in an oven at 110 C. for 2 hours to cure thepolymer. The tubes were then cooled to 25 C., and broken to remove thespecimens, which were then trimmed to form test pellets in the form ofright cylinders approximately 0.70 inches in diameter X 0.85 inches inheight, the exact dimensions being measured and recorded. One pellet ofeach elastomer was submitted to the following procedure, usingchloroform as the swelling agent, and another pellet of the sameelastomer was submitted to the same procedure, using tetrahydrofurane asthe swelling agent. Each pellet was placed in a covered beakercontaining a sufficient quantity of solvent (chloroform ortetrahydrofurane as the case might be) to immerse the pellet, and thecovered beaker stored for 4 days at a temperature of 25 C. Those of thepellets which were immersed in chloroform were manually turned over eachday to insure even exposure, as they tended to float in this solvent. Itwas made certain before proceeding further with the determination thatthe pellet contained imbibed therein at least percent by volume ofsolvent.

Each of the resultant swollen test pellets was removed at the end of the4 days storage and tested in a compression test apparatus having twoparallel flat platens, arranged to be moved toward each other and tomeasure a. the extent of such movement in mils and b. the force inpounds opposing such movement. The pellet was placed in with one flatface down in a shallow pan which contained the same solvent as that withwhich the pellet was swollen, and the pan set upon the lower platen ofthe apparatus. The upper platen was then moved down into contact withthe upper flat face of the test pellet, which downward movement was thencontinued while simultaneously measuring the distance of the movementand the force resisting the movement. These pairs of values for thepellet under test were then plotted on graph paper to yield astress-strain curve (pounds ordinate vs. mils abscissa) having astraight line portion, and the slope of this straight line portion wasthen measured and used in the calculations to follow.

Cluff et al., 100. cit., give the following approximate formula for thecross-linking density as determined in their apparatus.

S;;- (178,500) -he 2.54).4

.001199-sB- ho], D2 where:

S the stress-strain slope in British units of pounds per mil ho B theunswollen height of the test pellet in British units of inches D theunswollen diameter of the test pellet in British units of inches. Themolecular weight M between cross-links was taken as the reciprocal of v/V, i.e.,

Accordingly as the determination was made with chloroform ortetrahydrofurane as the swelling agent, the M was recorded respectivelyas being between electrostatic cross-links or as being between covalentcross-links.

EXAMPLE I 300 grams (mixed isomers; "Hylene T", manufactured by E. I.deNemours and company) A series of prepolymers was prepared inaccordance with the foregoing recipe, as set forth in Table Ihereinafter. In each preparation there was employed a 2-liter roundbottom flask provided with a rotary stirrer operating through a vacuumseal, and with a connection for the introduction of nitrogen and pullingof vacuum. In each run, the glycol was charged into the flask, a vacuumof 3-5 mm absolute applied, stirring commenced and the contents heatedat 80 C. for 4 hours to dehydrate the material, after which the mass wascooled. The flask was flooded with nitrogen and the calculated amount oftolylene diisocyanate, 2 mols per mol of the glycol, was poured into theglycol in the flask, with stirring and maintenance of the blanket ofnitrogen in the free space above the glycol. When heat evolution hadsubsided, the flask was reclosed, the vacuum reapplied, and the contentsstirred and heated for 1 hour, after which the mass was cooled to 25 C.

B. Final Compounding and Curing Prepolymer 200 g.

(prepared as above described) MOCA .80 1.10

(methylene bis-o-chloroaniline) Each of the prepolymers prepared asabove described was then compounded and cured into test specimens inaccordance with the foregoing recipe. Based on the NCO analysis for theparticular prepolymer, the amount of MOCA sufficient to provide theratio of equivalents of MOCA/equivalent of NCO selected for thatprepolymer was weighed out, melted, and rapidly introduced into theprepolymer in the original equipment. Vacuum was reapplied, the mixturestirred for 2 minutes, the vacuum released, and the mixture cast intomolds patterned for various physical tests to be made thereon. Themixture was cured in the molds in an oven at 250 F. (121 C.) for 2hours, and

M D 3 the cured specimens then cooled and subjected to S hoB' (.001199)physical tests as set forth herewith in Table I.

TABLE 1 Vulcanizate properties Molecular Weight MOCA used betweenPhysical properties at 212 F;

Equiv- Electr Crescent 5% alents stat Tensile tear Elonga- 300% modulusRun per mol Covalent strength strength tion modulus at 25 C No Grams N Oerosslluks (p.s.1.) (lb./in.) (percent) (p.s.i.) (p.s.i.)

(3&1 0. 2, 500 1, 430 241 170 396 72. 2 0. 1,180 3, 150 1, 695 67 270420 76.1 0. l, 300 5,050 2, 030 282 350 1 710 425 80. 2 1.00 5, 2, 550205 400 l, 830 430 84. 2 1.05 2,000 348 505 l, 620 464 so. 0 1.10Soluble 1,085 30!: 000 1.110 4 10 This polymer was soluble in thetetruhydrofurene, and hence the determination could not be mm EXAMPLE IICAST TIRE A. Tread Compound Prepolymer 5.5 lb.

(prepared by reacting Polymeg 2000" (2500 grams) a po1y(propyleneglycol) of molecular weight 2000, manufactured by the'Quaker OatsCompany with Hylene T" tolylene diisocyanate in a mol ratio of 2 molsdiisocyanate/mol po1y(propylene glycol) Silicone oil 2 grams (DC200, aproduct of Dow-Corning Company) Epoxy resin/carbon black blend 50 grams(V-780 a product of Ferro Corp.) MOCA 380 grams B. Body CompoundPrepolymer 16 pounds (as at A" above) (7270 grams) Silicone oil 7 grams(as at A above) Epoxy rosin/carbon black blend 182 grams (as at A"above) Di(2-ethyl hexyl) phthalate 1450 grams MOCA 1464 grams Each ofthe above compounds was prepared separately and injected into acentrifugal tire mold, the tread compound being injected first to formthe tread, and the body compound being injected second to form the bodyof the tire.

The above recipe corresponds to Run No. in Table I above. For eachcompound, there was provided a 20- gallon stainless steel pressurevessel provided with a power stirrer, a heating and cooling jacket,connections for supplying nitrogen and for pulling a vacuum in the freespace of the vessel, and a valved discharge conduit at the bottom of thevessel. The prepolymer and all ingredients except the MOCA were chargedtogether into the vessel under a blanket of nitrogen, and the vesselclosed. A vacuum of 3-5 mm. absolute was then pulled on the vessel, andthe contents agitated and heated at 162 F. (72 C.) for 2 hours, afterwhich the vessel was opened and the free space in the vessel floodedwith nitrogen. The MOCA was melted, supercooled to 99 C. and added tothe vessel with stirring. The vacuum was then reapplied, and. themixture stirred for 3 minutes. Nitrogen pressure was then introducedinto the vessel, and the contents blown out through the dischargeconduit into a mold having, together with a collapsible core therein, aconfiguration complementary to a Firestone DeLuxe Champion 7.35:14 tire,and rotating about its axis at 700 rpm in a removable oven enclosuremaintained at 250 F. The tread compound was blown in first and settledin the peripheral portions of the mold to form the tread portion asindicated at 16 in FIG. 1 of the drawing, and the body compound wasblown in second to fill up the remainder of the free space in the moldto form the body portion 12, 13. The rotation and oven temperature weremaintained for 2 hours, after whichthe oven enclosure was removed andthe rotation continued in open air to cool the mold. At the end of thistime, the rotation was stopped, and the tire stripped from the moldv'lires made as described above were subjected to the Department ofTransportation Tests in accordance with the Motor Vehicle SafetyStandards No. 109. The tire subjected to the endurance portion of thetest, went 1,365 miles. The tire subjected to the high speed test, inwhich the speed is progressively increased over time, went to 125 milesper hour over a period of 0.8 hours.

EXAMPLE III CAST TIRES RANGE (OF AMINE A. Tread Compounds Prepolymer 100parts (Adiprene L-l00" a po1y(propylene by weight glycol) originallyhaving a molecular weight of 1000, end-capped with tolylenediisocyanate. NCO content 4.1%. Product of E. I. duPont deNemours & Co.)

Silicone Oil 0.1 part (DC-200" a product of Dow by weight CorningCompany) Epoxy Resin/Carbon Black Blend 2.0 parts (V-780, a product ofby weight Ferro Corp.)

MOCA 12, 13 or 14 parts by weight B. Body Compounds Prepolymer 100 parts(Adiprene L-167" a poly(propy1ene by weight glycol) originally having amolecular weight of, end-capped with tolylene diisocyanate, NCO content6.3%; product of E1. duPont deNemours & Co.)

Silicon Oil 0.1 part (DC-200) by weight Epoxy Resin/Carbon Black Blend2.5 pans ("V-780) by weight Di(2-ethyl-hexyl)phthalate 20 parts byweight MOCA 19, 20 or 21 parts by weight A series of tires was cast fromcompositions in accordance with the foregoing recipe, using theprocedure of Example 11 and varying the proportion of MOCA as indicatedin connection with the various tires as listed hereinafter. Alsospecimens for various laboratory tests were also cast from the variouscompositions. The tread composition containing; 14 parts of MOCA, andthe body stocks containing 21 parts of MOCA, provide a ratio ofequivalents of MOCA/equivalents of NCO of approximately 1.06.

Tire Durability Four tires were cast in which the MOCA was varied in thestocks as indicated in Table I]. These tires were run to failure on theRMA endurance test, with results as follows.

TABLE II Equivalent Endurance Tire Ratios (miles) No. MOCA Used (parts)MOCA NCO In In In In Trfiad y Tread Body The superiority of the tireshaving a MOCAzNCO of 1.0 is quite striking.

Cut Growth Tires were prepared, using a body stock containing 21 partsof MOCA, and varying the MOCA in the tread stock as indicated in Table111. The tires were subjected to the V.E.S.C. cut growth test, in whicha total of 16 /4 inch starting cuts are made in the bottom of the treadgrooves, the tire run on a test drum for a specified time, and the totalincrease in length of the cuts measured and taken as the crack growth.The greater the increase, the poorer the cut growth resistance of thestock is considered. Following are the results.

TABLE 111 MOCA Ratio Crack Tire in tread MOCA: Growth No.

(parts) NCO (inches) Again the superiority of the tires according to thepresent invention is unequivocal.

Flex Data DeMattia flex specimens were prepared from the several stocks,and subjected to the DeMattia flex test at 176 C. Following are theresults.

(a)'l"hese body stocks were made from the recipe for body stocks at thehead of this example, except that the di(2-ethylhexyl)phthalate wasomitted.

(b)These body stocks were made in full accordance with the recipe forbody stocks at the head of this example.

Cuttability A series of body stocks were made in accordance with thebody stock recipe and procedure, except that the ratio of equivalents ofMOCA to equivalents of NCO in the prepolymer were varied as indicated inTable V. These stocks were subjected to a test in which a slab of thecured stock 5 X 1% X inches is placed upon a flat support with one ofthe 5 X 1% inches faces down. A ram carrying an anvil having a face 1%inches long and one thirty-second inch wide moves down and forces theanvil into the upper face of the slab. The load required to force theanvil completely through the slab is taken as the cuttability rating ofthe stock. Following are the results.

TABLE V Ratio of Equivalents of MOCA to Equivalents Rating No.

of NCO From the foregoing description and detailed specific physicalexamples, it will be evident that this invention provides novelpneumatic tires, air springs, hoses, power transmission belts and otherarticles which are subject to tensile stresses and dynamic flexure inservice, which service the articles withstand wholly or largely withoutthe complication of cord reinforcements. The articles can be made bylabor-sparing and rapidthroughput processes, from convenientlyobtainable and inexpensive starting materials. Tires in accordance withthe invention are substantially free of time-dependent changes inconfiguration and properties, withstanding inflation at customarypressures without undue or uneven expansion, and without creep ordeterioration of physical properties over a duration of time required ofa tire in use. The tires are resistant to cuts, breaks and other roaddamage in service, and are highly resistant to out growth, abrasivewear, and failure from flexure.

What is claimed is:

1. A tire I. a portion at least of the walls of which A. are withoutreinforcing fabric and B. are constituted of 1. a vulcanized elastomerhaving a. tensile strength at 212 F. 21,800 psi b. crescent tearstrength at 212 F. 2200 psi c. DeMattia flex life at 176 F. 22X10 cyclesand at ambient temperature (1. Modulus of elongation of 250-400 psi at 5percent elongation 1,l00-l,300 psi at percent elongation l,400-l ,550psi at 200 percent elongation 1,600-1 ,800 psi at 300 percent elongation2,000-2,200 psi at 400 percent elongation 2,8003,500 psi at 500 percentelongation e. Tensile strength 22,800 psi f. Elongation 2400 percent andg. Youngs flexural modulus l0,000l5,000

pm the vulcanized elastomer more particularly havmg h. a molecularweight of 8005,000 between electrostatic cross-links and i. a molecularweight of 5,l0040,000

between covalent cross-links.

2. A tire according to claim 1, wherein said elastomer is a polyurethaneelastomer.

3. A tire according to claim 2, wherein the elastomer is prepared from aprepolymer synthesized from substantially equimolecular proportions of apolyalkylene glycol and a diisocyanate, which prepolymer is thereafterreacted with 0.98 1.08 equivalents of diamine per equivalent ofisocyanate groups in the prepolymer.

4. A tire according to claim 2, wherein the elastomer is constituted ofpolyether chains connected to each other according to the repeatingscheme -[-PO-CONHR -C-NH--R NH --CO-NHR -Nl-lCOO-] wherein P representsa poly(alkylene ether) chain R, is the organic central group of adiisocyanate and R is the organic central group of a diamine.

5. A tire according to claim 4, wherein the polyether chain P is theresidue of poly(tetramethylene glycol).

6. A tire according to claim 1, which is cast by centrifugal castingfrom a liquid precursor of the elastomer and which tire has noreinforcing fabric in any portion thereof.

7. A tire according to claim 1, which is cast by centrifugal castingfrom a liquid precursor of the elastomer and which tire has reinforcingfabric in the read area thereof and has no reinforcing fabric in anyother portion thereof.

8. A tire according to claim 7, which is cast by centrifugal castingfrom a liquid precursor of the elastomer and which tire has reinforcingfabric in the tread area and a portion only of the sidewall area, saidportion being a portion contiguous to the tread area and has noreinforcing fabric in any other portion thereof.

2. A tire according to claim 1, wherein said elastomer is a polyurethaneelastomer.
 3. A tire according to claim 2, wherein the elastomer isprepared from a prepolymer synthesized from substantially equimolecularproportions of a polyalkylene glycol and a diisocyanate, whichprepolymer is thereafter reacted with 0.98 -1.08 equivalents of diamineper equivalent of isocyanate groups in the prepolymer.
 4. A tireaccording to claim 2, wherein the elastomer is constituted of polyetherchains connected to each other according to the repeating scheme -(-PO - CO - NH - R1 - NH - CO - NH - R2 - NH - CO - NH - R1 -NH - CO - O -)-wherein P represents a poly(alkylene ether) chain R1 is the organiccentral group of a diisocyanate and R2 is the organic central group of adiamine.
 5. A tire according to claim 4, wherein the polyether chain Pis the residue of poly(tetramethylene glycol).
 6. A tire according toclaim 1, which is cast by centrifugal casting from a liquid precursor ofthe elastomer and which tire has no reinforcing fabric in any portionthereof.
 7. A tire according to claim 1, which is cast by centrifugalcasting from a liquid precursor of the elastomer and which tire hasreinforcing fabric in the tread area thereof and has no reinforcingfabric in any other portion thereof.
 8. A tire according to claim 7,which is cast by centrifugal casting from a liquid precursor of theelastomer and which tire has reinforcing fabric in the tread area and aportion only of the sidewall area, said portion being a portioncontiguous to the tread area and has no reinforcing fabric in any otherportion thereof.